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He expresses regret for how "gun walking" investigations have been handled

"Gun walking" has led to hundreds of firearms' being lost or unaccounted for

For the first time, a top official of the Obama administration's Justice Department has expressed regret for the way the department handled the controversial tactics of allowing "gun walking" in firearms investigations by agents of the Bureau of Alcohol, Tobacco, Firearms and Explosives.

After months of Justice Department executives staunchly defending what they said was their minimal role in flawed ATF operations, and denials of high-level involvement, Assistant Attorney General Lanny Breuer issued a statement Monday acknowledging his actions in the case.

"Knowing what I now know was a pattern of unacceptable and misguided tactics used by the ATF, I regret that I did not alert others within the leadership of the department to the tactics used in Operation 'Wide Receiver' when they first came to my attention," Breuer said.

Breuer first learned in April 2010 of the tactic used by the ATF.

Operation "Wide Receiver," which began in 2006, like the controversial "Fast and Furious," which began during the Obama administration, allowed illegally purchased firearms to "walk" from gun stores in Arizona across the Mexican border into the arms of drug cartels. The agents intended to monitor the trafficking and trace the flow of weapons, but hundreds were lost or unaccounted for.

The tactic led to a storm of outrage inside and outside the ATF when two of the missing weapons were found at the site where Border Patrol agent Brian Terry was murdered last December.

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Breuer said he had also failed to recognize the same tactics were used again in "Fast and Furious".

"I did not draw a connection between the unacceptable tactics used by the ATF years earlier in Operation Wide Receiver and those in Operation Fast and Furious, and therefore did not alert others within department leadership of any similarities between the two. That was a mistake and I regret not having done so," Breuer said in a written statement.

Breuer faces a Senate subcommittee hearing Tuesday in which he may be asked for a face-to-face explanation of his position.

As head of the criminal division, Breuer is one of Attorney General Eric Holder's most important assistants.

His statement of regret came as the Justice Department sent 650 pages of documents to congressional investigators. The documents had been subpoenaed October 11 by Republican lawmakers angered by what they claim was stonewalling by the Justice officials.

Senate Judiciary Committee ranking member Charles Grassley, R-Iowa, said his staff would scour the new documents.

"At first glance, the documents indicate that contrary to previous denials by the Justice Department, the criminal division has a great deal of culpability in sweeping the previous Wide Receiver strategy under the rug and then allowing the subsequent Operation Fast and Furious to continue without asking key questions," Grassley said.

"With every document that comes out, the Justice Department loses credibility and the faith of the the American people," Grassley concluded.